Moving metal

Johan de Nysschen, executive vice president in charge of Audi of America, couldn't be much more plain about it: "This is the most important car in our lineup." He's talking about the A4. In the Audi lineup, the A4 is pretty much in the middle. There are the R8, A8, A6, A5, and Q7 above it. There is the A3 below it. And there are the TT and forthcoming Q5 crossover aligned with it. In the U.S., Audi moves some 40,000 A4s per annum. It is also, in de Nysschen's words, "our foundation" in Germany, as well, accounting for some half of the brand's sales.

All of which is to say that the car is rather significant. Not as sexy and stylish as the R8 (but then few cars are) and not as frugal and functional as the A3 (which, after all, is the entry into the brand), the A4 is the sort of car that cannot be underestimated to the growing success of the brand. Which undoubtedly makes the all-new 2009 A4 all the more important in that it must be a car that advances things on the one hand but mustn't lose its partisans on the other.

Big(ger)

Known in the company parlance as the B8, the '09 A4 is, perhaps not surprisingly, bigger than its predecessor, the B7. That is, the overall length of the new car is 185.2 in., which is up 4.6 in. The 110.6-in. wheelbase is 6.5 in. greater than that of the B7. The front overhang, 34.1 in., is actually 2.7 in. shorter than the previous model. The rear overhang, at 40.5 in., is up a bit, 0.7 in. The vehicle is wider, as well: 71.9 in., up 2.1 in. The height stays the same at 56.2 in., but when you take the width into account, the vehicle is proportionately lower than the B7.

In fact, despite the fact that the frontal area of the '09 sedan is bigger than its predecessor (23.68-ft2 compared with 23.03-ft2), the aero has been improved: the drag coefficient is a relatively sleek 0.27, bettering the previous 0.31. (Not only did they pay careful attention to the air moving over the visible sheet metal, but they also made the underside of the car as flat as practical.)

The competitors include the BMW 3 Series and the Mercedes C Class; the A4 is dimensionally larger than both of those vehicles, with the exception of the height of the C Class, which is 57 in.

Visible

Visually, the sedan is more coupe-like than its predecessor, particularly as there is a longer hood and the cabin is consequently visually pushed back. Looked at front on, the single-frame grille-stone gray on the models with the new 2.0-liter four; high-gloss black on the 3.2-liter V6 models-is lower and wider than the previous model's. What's more, the A4 is available with xenon headlights; each of the lights has 14 white LEDs that serve as the daytime running lights (halogen lights with incandescent running lights are also available, although these are certainly not as striking at the others).

De Nysschen calls the A4 "the most visible car for Audi in the U.S." Clearly, that has to do with the number of vehicles (e.g, the R8 is arguably the most visually striking car for Audi anywhere in the world). But as a sedan, it is visually stylish.

Materially different

Audi is well known for its expertise in aluminum. And there is aluminum used on the A4. There are aluminum suspension components, such as the engine and front suspension subframe, the single largest chassis component. The 265-hp 3.2-liter FSI engine has an aluminum block and head; the new turbocharged, 211-hp 2.0-liter TFSI, has an aluminum alloy cylinder head (and a cast iron block). But the aforementioned aluminum expertise relates to the body and structure.

The A4 is not an aluminum car. But what's somewhat striking is that even the top U.S. Audi executive, de Nysschen, notes the fact that there is an extensive use of ultra-high-strength steel (UHSS). This is not the sort of thing that is typically glossed by someone with their eye on business and sales, not structural engineering. Yet the use of the material is absolutely notable, and contributes to a rigid body structure, as well as enhancing safety.

There is the use of hot-formed boron alloyed steel blanks to produce various components. In the hot forming operation, the blanks are heated to 1,742°F, formed, and quenched. The resulting tensile strength of the component is as much as 1,600 mPa. Among the ultra-high-strength steel applications are the center tunnel, inner sills, B-pillars and firewall transverse beams. Overall, about 12% of the body-in-white is made of hot-formed UHSS; 18% is UHSS; 32% is high-strength steel; and 38% is conventional deep-drawing steel grades.

Spots, bonds and brazes

And just as the use of aluminum for the famed Audi Space Frame (ASF) gave rise to the use of alternative joining methods, the same is true for the A4. Spot welding is used, but whereas there were approximately 6,500 spots in the B7 version, there are 5,500 in the B8. However, the amount of adhesive bonding has jumped from 26 m to 125 m. In addition to which there is MIG, MAG, and laser welding, as well as plasmatron brazing.

Audi is working to increase its sales in the U.S. and other markets around the world. It is working to establish itself as a German vehicle manufacturer that is considered in the same space as Mercedes and BMW. And with the A4, in terms of design and engineering, it has gone a long way in establishing its credibility and credentials.

How to increase the length of the wheelbase

To achieve the longer wheelbase in the modular MLB platform that’s used for the A4 (as well as the A5), Audi engineers moved the front axle forward. But in order to do that, they had to move something else. Actually, three somethings. Specifically, they moved the differential forward by 6.06 in. such that it is located directly behind the engine—which meant that they had to put the torque converter (or clutch) back where the differential had been. And because there was a change in weight balance, the battery was moved out from under the hood back to the rear cargo area.